networking

 The network is a crucial component of
today’s computing systems.
 Resource sharing across networks has taken
the form of multitier architectures having
many different servers.
 If you think of a computing system as
collection of workstations and servers, then
surely the network is the transportation of this
configuration.

 A network is, fundamentally, a system of
senders and receivers – a common feature
of any communication system.
 The sender, or source, is a computer which
sends information to another.
 The receiver, or destination computer, is the
computer to which the information is sent.
 Any machine capable of communicating on
the network is a device or node.

There are THREE types of network available
 Local Area Networks (LAN)
 Wide Area Networks (WAN)
 Metropolitan Area Networks (MAN)

 Used in small geographical areas like Building or
Campus.
 Offer high-speed communications (10/100/1000Mbps)
 Provide access to many devices
 Use LAN-specific devices such as Hubs, Switches
and network interface cards

 Cover large areas – may span the world
 Compared to LANs – slow speed communication
 Access to WANs is limited – a LAN will access a WAN
through a single point (often a bottleneck)
 Will use devices such as routers, modems and WAN
switches

 Made up of LANs which are interconnected across a
metropolitan area
 Also may appeal to regional businesses
 Gives access speeds in hundreds of megabits per
second (or even gigabits speeds)
 Uses a single connection point to connect LANs
 As well as using routers will also use switches

 Bus Topology
 Ring Topology
 Star Topology
 Mesh Topology

 Network maintained by a single cable
 Cable segment must end with a terminator
 Uses thin coaxial cable (backbones will be thick
coaxial cable)
 Extra stations can be added in a daisy chain manner

Advantages
 Inexpensive to install
 Easy to add stations
 Use less cable than
other topologies
 Works well for small
networks
Disadvantages
 No longer recommended
 Backbone breaks, whole
network down
 Limited no of devices
can be attached
 Difficult to isolate
problems
 Sharing same cable
slows response rates

 No beginning or end (a ring in fact !!)
 All devices of equality of access to media
 Single ring – data travels in one direction only, guess
what a double ring allows !?
 Each device has to wait its turn to transmit

Advantages
 Data packets travel at
great speed
 No collisions
 Easier to fault find
 No terminators required
Disadvantages
 Requires more cable
than a bus
 A break in the ring will
bring it down
 Not as common as the
bus – less devices
available

 Like the spokes of a wheel (without the symmetry)
 Centre point is a Hub
 Segments meet at the Hub
 Each device needs its own cable to the Hub
 biggest type of topology
 Easy to maintain and expand

Advantages
 Easy to add devices as the
network expands
 One cable failure does not
bring down the entire
network (resilience)
 Hub provides centralised
management
 Easy to find device and
cable problems
 Can be upgraded to faster
speeds
Disadvantages
 A star network requires
more cable than a ring or
bus network
 Failure of the central hub
can bring down the entire
network
 Costs are higher
(installation and
equipment) than for most
bus networks

 Not common on LANs
 Most often used in WANs to interconnect LANS
 Each node is connected to every other node
 Allows communication to continue in the event of a
break in any one connection
 It is “Fault Tolerant”

Advantages
 Improves Fault
Tolerance
Disadvantages
 Expensive
 Difficult to install
 Difficult to manage
 Difficult to troubleshoot

 Hubs
 Bridges
 Switches
 Routers

 A central point of a star topology
 Allows the multiple connection of devices
 Can be more than a basic Hub – providing additional
services (Managed Hubs, Switched Hubs, Intelligent
Hubs)
 In reality a Hub is a Repeater with multiple ports
 Functions in a similar manner to a Repeater
 Works at the Physical Layer of the OSI model
 Passes data no matter which device it is addressed to

 Advantages – Cheap, can connect different media
types
 Disadvantages – Extends the collision domain, can
not filter information, passes packets to all connected
segments

 Like a Hub it connects segments
 Works at Data Layer – not Physical
 Uses Mac address to make decisions
 Acts as a ’filter’, by determining whether or not to
forward a packet on to another segment
 Builds a Bridging Table, keeps track of devices on
each segment
 It forwards packets whose destination address is on
a different segment from its own
 It divides a network in to multiple collision domains –
so reducing the number of collisions

 Advantages – Limits the collision domain, can extend
network distances, uses MAC address to filter traffic,
eases congestion, can connect different types of
media, some can connect differing architectures.
 Disadvantages – Broadcast packets can not be
filtered, more expensive than a repeater, slower than
a repeater – due to additional processing of packets.

 A multiport Bridge, functioning at the Data Link Layer
 Each port of the bridge decides whether to forward
data packets to the attached network
 Keeps track of the Mac addresses of all attached
devices (just like a bridge)
 Acts like a Hub, but filters like a Bridge
 Each port on a Switch is a collision domain

 Advantages - Limits the collision domain, can
provide bridging, can be configured to limit broadcast
domain
 Disadvantages – More expensive than a hub or
bridge, configuration of additional functions can be
very complex

 Works at Network Layer in an intelligent manner
 Can connect different network segments, if they are
in the same building or even on the opposite side of
the globe
 Work in LAN, MAN and WAN environments
 Allows access to resources by selecting the best
path
 Can interconnect different networks – Ethernet with
Token Ring
 Changes packet size and format to match the
requirements of the destination network

 Advantages – Limits the Broadcast domain, can
function in LAN or WAN, connects differing media
and architectures, can determine best path/route,
can filter broadcasts
 Disadvantages – Expensive, must use routable
protocols, can be difficult to configure (static routing),
slower than a bridge

 The OSI model was developed to enable different
manufacturers networking products to work together.
 For a variety of reasons, the model was never widely
implemented.
 However it is used widely in colleges to teach
network layers and by companies to describe their
products.
 The OSI reference model defines 7 layers for network
communication - each layer defines a particular
network function.

 It breaks network communication into smaller simpler
parts.
 It standardizes network components to allow multiple-
vendor development and support.
 It allows different types of network hardware and
software to communicate with each other.
 It prevents changes in one layer from affecting the
other layers, so that they can develop more quickly.
 It breaks network communication into smaller parts to
make learning it easier to understand.

 The lowest, bottom, layer – responsible for the
physical connection between devices
 The NIC converts the data (bits) in to transmission
signals.
 Transmissions may be analogue or digital
 Responsible for the rate of transmission
 Includes all components such as the type of
connector (RJ-45, Token Ring, BNC, SC connector)
 Devices at this level include NICs, repeaters, hubs
and concentrators

 The data link is responsible for node to node validity
and integrity of the transmission
 The data link layer uses MAC, or hardware addresses
for communication.
 LAN communications, each machine on the same
connected media type needs a unique MAC address.
 A MAC address is 48 bits as 12 characters length in
hexadecimal number.

 Each host on segments needs a unique host number
from within the assigned network number. (IP
Address)
 The combination of the network and host number
assigned to a device provides a unique layer-3
address throughout the entire network.
 IP is 32 Bit Dotted decimal Number.
 The network layer supports both connection-orientated
and connectionless service from higher-layer
protocols.
 Network-layer protocols typically are routing protocols.

 It sets up and maintains a session connection between
two devices.
 It can provide for the reliable or unreliable delivery of
data across this connection. (TCP, UDP)
 Transport-layer functions typically include flow control,
virtual circuit management (Ports or Threads), and
error checking and recovery using checksum.
 Ensure Delivery of entire file or message
 The lowest layer that have any awareness of Network

 The Session layer arbitrates the dialogue between two
communicating nodes, opening and closing that
dialogue as necessary.
 It controls the direction and mode (half -duplex or full-
duplex).
 It also supplies recovery checkpoints during file
transfers.
 Responsible for
 Handshaking, Keep alive message, Session
termination
 Dialog Control (Simplex, Half duplex, Full Duplex)
 Example : NFS, SQL, RPC

 When data are transmitted between different types of
computer systems, the presentation layer negotiates
and manages the way data are represented and
encoded.
 For example, it provides a common denominator
between ASCII and EBCDIC machines formats.
 Tasks like Data Compression, Decompression,
Encryption, Decryption are associated with this layer.
 Also associated with Multimedia operations.
 Examples of presentation layer protocols and
standards include ASCII, BMP, GIF, JPEG, WAV, AVI,
and MPEG.

 ‘Closest’ layer to the user
 Works with the applications you use to communicate
over the network
 This interface can be command-line-based or
graphics-based.
 The most common are telnet, FTP, web browsers, and
e-mail.

 One of the most important protocols.
 Main purpose is to provide logical addressing through
the use of an IP address.
 Uses IP address to route information between
networks, therefore every device requires a unique
address.
 Developed to function within a UNIX environment in
the days of ARPAnet.

 require connect different network segments.
 Routing can be done over the LAN, WAN or MAN
 Routing table is use to route the packet across the
networks.
 Route added can be added 2 ways.
 Static Routes : routes are manually configured by a
network administrator.
 Dynamic Routes : adjust automatically to changes in
network topology, and information it receives from
other routers.

networking

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